Scrappage shmackage

A scrappage scheme is being raised as a way of getting old clangers off the road to be replaced with new cars. The government would give you $2000 to scrap your old falcon on the condition you bought a new car. Superficially this might have some appeal but if analysed it seems like a terrible idea. A cash grab by an industry that has failed to see the writing on the wall. This is a good example of why a broad based market mechanism, like carbon trading or a carbon tax is needed to find where the most cost effective savings can be made. A scrappage scheme could cost us a lot of money and achieve no reduction at all, because it doesn't necessarily reduce total emissions it just updates the fleet. It's dependent on the cars producing less total emissions, so the cars would have to be smaller on average than the ones they replace and the total distance travelled would also have to be held at a constant. Are people tempted to drive their new cars more?